1. Field of the Invention
One or more embodiments of the present invention relate to cost effective structural rehabilitation and enhancement.
2. Description of Related Art
Structural integrity of reinforced concrete structures is severely compromised due to spalling. In general, spalling is caused due to corrosion of the reinforcement, which is generally a reinforcing bar (or rebar for short) that is a metal or a metallic alloy most likely comprised of steel. When the reinforcement corrodes, it rusts (and crumbles) and therefore, expands in volume within the concrete structure, causing spalling. Additionally, loose pieces of rust particles (or crumbles) of the reinforcement also cause the concrete structure to lose its mechanical bond with the reinforcement, making the reinforcement ineffective. A further issue with corrosion of the reinforcement is that as the reinforcement corrodes into crumbling rust, the amount of reinforcement left is degraded, weakening the structural integrity of the reinforced concrete structure.
Conventional methods for repairing of spalled reinforced concrete structures vary greatly dependent on the amount of spalling of the reinforced concrete structure, the amount of corrosion of the reinforcement, and overall budgeted cost for repair. In general, the conventional repairing processes of spalled reinforced concrete structures involved many labor-intensive steps that are complex and require skilled labor, which adds to the overall cost of the structural rehabilitation.
In general, conventional methods of repair require excavation of the concrete structure to reach the corroded rebar. It should be noted that the size of the excavation (the cavity) should be sufficiently large to expose rebar beyond the corroded portion. That is, the excavation size should be large to reach the portion of the rebar where no corrosion is observed. Additionally, if the extent of the corrosion of the rebar observed is severe (e.g., where the integrity of the rebar is fully compromised, making it ineffective), the cavity should be further extended axially along the rebar to expose even more of the non-corroded portion thereof to enable augmentation of the rebar using well known splicing methodologies (detailed below).
Once the appropriate axial length of rebar is fully exposed, the formed cavity is cleaned from debris such as loose concrete. Further, the rebar is also completely cleaned from debris, loose rust, and any visible corrosion. That is, the rebar must be completely cleaned from any corrosion until a non-corroded portion of the rebar (the actually clean, bare steel portion) is reached. Therefore, to completely clean the rebar from rust or any corrosion, excavated cavity must also be of sufficient depth to enable access and reach to the entire surface of the exposed rebar from all directions and not just the “front” viewable portion. It should be noted that completely cleaning of the rebar from corrosion and removal of all rust (e.g., by scraping) is very time consuming and labor intensive. If the rebar is fully compromised, the compromised portion must be cut out completely and augmented.
The augmentation of a rebar is a complex, labor intensive, and time-consuming process that uses well known splicing methodologies, resulting in a lap spliced rebar. In general, the conventional methods for augmentation of a rebar require that the fully compromised portion of the rebar to be cut-off, and the remaining non-corroded exposed portions thereof be of sufficient axial length to allow for splicing (e.g., lap splicing). Therefore, the cavity itself must be enlarged to expose sufficient axial length of the non-corroded portion of the rebar to allow for proper lap splicing, resulting in continuous line of reinforcement that meet the required tensile strengths.
After cleaning the rebar and cavity from loose debris (rust or loose concrete), and if required, augmenting the rebar, corrosion protection (anti-corrosion) is applied to the rebar (and the augmented rebar). Thereafter, a primer (sealant/adhesive bonding material) is applied to the surface of the excavated cavity to seal and provide a bonding surface, which facilitates bonding of mortar (detailed below) with the surface of the cavity.
Thereafter, various methods are used to actually close off the cavity. For conventional methods, if the cavity is small, it is generally more cost effective to patch the cavity using well-known methodologies such as multi-lift patching, which itself is very time consuming, especially if the number of repairs is large. The quality of multi-lift patching process is generally poor due to potentially weak bonding properties between patched layers. Weak bonding properties are generally caused by variations in densities of the patching layers, temperature variation between a patched layer and a next layer, moisture variations, which affect viscosity of subsequent layers, etc.
In conventional methods, if the cavity is large, it is generally more cost effective to pour mortar into a larger excavated cavity to close off the exposed rehabilitated rebar. However, prior to pouring of the mortar, forming structures are used for forming the poured mortar to fill the excavated cavity and allow the mortar to be cured flush with exterior surface of the concrete structure, which requires time and materials to construct.
In general, the forming structures used to form (or shape) the mortar are comprised of structures that are built to fit over and cover the excavated cavity. Accordingly, if the forming structure is comprised of wood for example, the appropriate thickness and size of wood must first be selected. Thickness and size depend on the amount of load to be supported by the forming structure. In addition to selecting the correct thickness and size, the actual wooden forming structure constituting the wood form itself must be engineered and built to enable the correct forming or shaping of the mortar. This is especially difficult for non-flat surfaces such as reinforced concrete support columns that are generally cylindrical and hence, the wood forming structure must somehow be built to enable the mortar to be flush with the surface of the cylindrically or other odd-shaped structures.
After selection of the thickness, size, and building of the forming structure, a means must be devised to actually securely position and place the wooden forming structure over the cavity opening. This phase of the overall conventional rehabilitations process becomes complex if the opening is oriented at a direction where the forming structure must be secured against gravity. For example, the excavated cavity opening may be under a bridge where the opening faces “down” below the bridge or it may be vertically oriented at the side of support column. Accordingly, the process of securing the forming structure over the opening must account for supporting it in a secure position. As importantly, the securing means must also support the loads of both the forming structure and the mortar when poured within the cavity (detailed below). Therefore, the securing means must take the weight of the mortar in addition to the forming structure to support both.
Conventional methods of mounting and positioning forming structures depend on the type of material from which the forming structure is made (e.g., wood, steel, plastic, etc.). Normally, setting up a forming structure on a vertical or overhead surface requires support and mechanisms that include intricate bracing, wales, studs, stakes, pegs, screws, clamp supports, bars, etc. The work usually requires tying various pieces together, as well.
After designing a forming structure for the cavity and installing or mounting it to cover over the cavity, a hole is made on the forming structure itself to allow mortar to be poured within the excavated cavity via the hole. This phase becomes complex when the opening of cavity and or the hole is overhead (i.e., oriented such that the pour is against the gravity). Thereafter, there is a wait time until the mortar is cured after which, the forming structure must be removed. The removal of the forming structure is not a simple task as it may require heavy machinery and skilled labor.
It should be noted that in addition to the numerous labor-intensive operations to rehabilitate the reinforced concrete structure, additional care must be taken to ensure compatibility between materials used when rehabilitating the structure. For example, the type of corrosion protection material applied must be compatible with the type of mortar material used to fill the cavity or the type of primer used on the surface of the cavity. For example, the corrosion protection material used should not chemically interact with the mortar material, which may result in a degraded the integrity of both.
Accordingly, in light of the current state of the art and the drawbacks to current rehabilitation methods mentioned above, a need exists for a rehabilitation process that is much simpler, requires much less labor-intensive/skilled operations, and uses compatible material for most rehabilitation projects.